A first-transceiver for use in an antenna diversity scheme. The first-transceiver comprises a first-time/clock-generation-unit; a first-receiver; and a first-transmitter. The first-receiver is configured to receive a wireless second-alignment-signal from a second-transceiver with a second-time/clock-generation-unit. The wireless second-alignment-signal is representative of a state of the second-time/clock-generation-unit. The first-transceiver is configured to set the first-time/clock-generation-unit, based on the wireless second-alignment-signal, to reduce an alignment-error between the first-time/clock-generation-unit and the second-time/clock-generation-unit. The first-transmitter is configured to transmit a wireless first-transmission-signal, in accordance with the first-time/clock-generation-unit, as part of the antenna diversity scheme. The first-transmission-signal corresponds to a second-transmission-signal that is transmitted by the second-transceiver. The antenna diversity scheme comprises aligned transmission of both the first-transmission-signal and the second-transmission-signal.
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15. A method of operating a first-transceiver for use in an antenna diversity scheme, the method comprising:
receiving a wireless second-alignment-signal from a second-transceiver with a second-time/clock-generation-unit, wherein the wireless second-alignment-signal is representative of a state of the second-time/clock-generation-unit; and
setting the first-time/clock-generation-unit, based on the wireless second-alignment-signal, to reduce an alignment-error between the first-time/clock-generation-unit and the second-time/clock-generation-unit;
using a frequency synthesizer in the first-time/clock-generation-unit to provide, based on a clock-source signal from an oscillator, a carrier frequency to tuners of a transmitter and a receiver, a sampling frequency to a dac of the transmitter and an adc of the receiver, and a system timer frequency to a system timer;
transmitting a wireless first-transmission-signal, in accordance with the first-time/clock-generation-unit, as part of the antenna diversity scheme, wherein:
the first-transmission-signal corresponds to a second-transmission-signal that is transmitted by the second-transceiver; and
the antenna diversity scheme comprises aligned transmission of both the first-transmission-signal and the second-transmission-signal.
1. A first-transceiver for use in an antenna diversity scheme, the first-transceiver comprising:
a first-time/clock-generation-unit;
a first-receiver, configured to receive a wireless second-alignment-signal from a second-transceiver with a second-time/clock-generation-unit, wherein the wireless second-alignment-signal is representative of a state of the second-time/clock-generation-unit; and
a first-transmitter;
wherein:
the first-transceiver is configured to set the first-time/clock-generation-unit, based on the wireless second-alignment-signal, to reduce an alignment-error between the first-time/clock-generation-unit and the second-time/clock-generation-unit;
a frequency synthesizer in the first-time/clock-generation-unit is configured to provide, based on a clock-source signal from an oscillator, a carrier frequency to tuners of the transmitter and the receiver, a sampling frequency to a dac of the transmitter and an adc of the receiver, and a system timer frequency to a system timer; the first-transmitter is configured to transmit a wireless first-transmission-signal, in accordance with the first-time/clock-generation-unit, as part of the antenna diversity scheme, wherein:
the first-transmission-signal corresponds to a second-transmission-signal that is transmitted by the second-transceiver; and
the antenna diversity scheme comprises aligned transmission of both the first-transmission-signal and the second-transmission-signal.
11. A multi-transceiver system comprising:
a first-transceiver comprising:
a first-time/clock-generation-unit;
a first-receiver, configured to receive a wireless second-alignment-signal from a second-transceiver with a second-time/clock-generation-unit, wherein the wireless second-alignment-signal is representative of a state of the second-time/clock-generation-unit; and
a first-transmitter;
wherein:
the first-transceiver is configured to set the first-time/clock-generation-unit, based on the wireless second-alignment-signal, to reduce an alignment-error between the first-time/clock-generation-unit and the second-time/clock-generation-unit;
a frequency synthesizer in the first-time/clock-generation-unit is configured to provide, based on a clock-source signal from an oscillator, a carrier frequency to tuners of the transmitter and the receiver, a sampling frequency to a dac of the transmitter and an adc of the receiver, and a system timer frequency to a system timer; the first-transmitter is configured to transmit a wireless first-transmission-signal, in accordance with the first-time/clock-generation-unit, as part of the antenna diversity scheme, wherein:
the first-transmission-signal corresponds to a second-transmission-signal that is transmitted by the second-transceiver; and
the antenna diversity scheme comprises aligned transmission of both the first-transmission-signal and the second-transmission-signal,
the second-transceiver, and
a digital communication channel configured to exchange coordination-signalling between the first-transceiver and the second-transceiver to co-ordinate setting the first-time/clock-generation-unit and/or the second time/clock-generation-unit.
2. The first-transceiver of
3. The first-transceiver of
4. The first-transceiver of
applying an offset to a count of the system timer;
applying a frequency offset to one or more of:
the carrier frequency that is provided to the tuners of the transmitter and the receiver,
the sampling frequency that is provided to the dac of the transmitter and the adc of the receiver,
the system timer frequency that is provided to the system timer;
tuning a crystal oscillator that is associated with the frequency synthesizer;
changing divider settings of a phase locked loop that is associated with the frequency synthesizer;
digitally rotating digital samples for compensating an RF carrier frequency offset; and
resampling of a digital signal for compensating a difference in DA converter frequency.
5. The first-transceiver of
6. The first-transceiver of
7. The first-transceiver of
if the alignment error is greater than a predetermined threshold, then the first-transceiver is configured to set the first-time/clock-generation-unit based on the wireless second-alignment-signal.
8. The first-transceiver of
receive a plurality of wireless alignment-signals, including the wireless second-alignment-signal, from a plurality of other transceivers, including the second-transceiver; and
set the first-time/clock-generation-unit, based on the plurality of wireless alignment-signals, to reduce alignment-errors between the first-time/clock-generation-unit and a plurality of time/clock-generation-units of the other transceivers.
9. The first-transceiver of
10. The first-transceiver of
12. The multi-transceiver system of
a time-of-transmission of the second-alignment-signal;
a value of the second-time/clock-generation-unit at a predefined moment in time relative to the time-of-transmission of the second-alignment-signal;
a value of the second-time/clock-generation-unit at a time-of-transmission of the second-alignment-signal;
a delay between the time-of-transmission and the time-of-reception of the second-alignment-signal;
an expected time of arrival of the wireless second-alignment-signal at the first-transceiver; and/or
an expected time of arrival of the wireless first-alignment-signal at the second-transceiver.
13. The multi-transceiver system of
(i) a timing-controller; and
(ii) the first-transceiver and the second-transceiver,
wherein the timing-controller is configured to provide the coordination-signalling to the first-transceiver and/or the second-transceiver to coordinate setting the first-time/clock-generation-unit and/or the second-time/clock-generation-unit.
14. The multi-transceiver system of
16. The method of
17. The method of
18. The method of
19. The method of
determining an alignment-error associated with the first-transceiver, and
setting the first-time/clock-generation-unit based on the wireless second-alignment-signal if the alignment error is greater than a predetermined threshold.
20. The method of
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This application claims the priority under 35 U.S.C. § 119 of European Patent application no. 18172503.7, filed on 15 May 2018, the contents of which are incorporated by reference herein.
The present disclosure relates to apparatus and methods for the alignment of transmissions, in particular, although not necessarily, transmissions provided by a distributed transceiver system designed for antenna diversity usage.
According to a first aspect of the present disclosure there is provided a first-transceiver for use in an antenna diversity scheme, the first-transceiver comprising:
Advantageously, such a first-transceiver can provide an alignment solution for an antenna diversity scheme that does not necessarily require an extra wired interface, any feedback from the receiving party, or the availability of a GPS signal or a base station.
In one or more embodiments, the first-transmitter is configured to transmit a wireless first-alignment-signal, representative of a state of the first-time/clock-generation-unit, for reducing an alignment-error between the second-time/clock-generation-unit and the first-time/clock-generation-unit.
In one or more embodiments, the first-transceiver is configured to set the first-time/clock-generation-unit by adjusting a time of the first-time/clock-generation-unit and/or a frequency of the first-time/clock-generation-unit.
In one or more embodiments, the first-time/clock-generation-unit comprises a frequency synthesizer and a system timer. The first-transceiver may be configured to set the first-time/clock-generation-unit by one or more of:
In one or more embodiments, the aligned transmission comprises transmission of both the first-transmission-signal and the second-transmission-signal aligned with respect to time and/or frequency such that they constructively combine when received at a remote receiver.
In one or more embodiments, the wireless second-alignment-signal comprises a prefix and/or a postfix portion of an earlier-second-transmission-signal. The earlier-second-transmission-signal may be transmitted before the second-transmission-signal.
In one or more embodiments, the first-transceiver my further comprise a controller configured to determine an alignment-error associated with the first-transceiver, if the alignment error is greater than a predetermined threshold, then the first-transceiver may be configured to set the first-time/clock-generation-unit based on the wireless second-alignment-signal.
In one or more embodiments, the first-transceiver is further configured to:
In one or more embodiments, the first-transmission-signal corresponds to the second-transmission-signal as both the first-transmission-signal and the second-transmission-signal comprise corresponding representations of an information-signal.
In one or more embodiments, the wireless second-alignment-signal is a wireless Radio Frequency signal.
There is also disclosed a multi-transceiver system comprising:
In one or more embodiments, the coordination-signalling comprises one or more of:
In one or more embodiments, the digital communication channel is connected between:
In one or more embodiments, the first-transceiver is spaced apart from the second-transceiver.
According to a further aspect, there is provided a method of operating a first-transceiver for use in an antenna diversity scheme, the method comprising:
There is also disclosed an electronic device or an integrated circuit comprising any first-transceiver or multi-transceiver system disclosed herein.
While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that other embodiments, beyond the particular embodiments described, are possible as well. Ali modifications, equivalents, and alternative embodiments falling within the spirit and scope of the appended claims are covered as well.
The above discussion is not intended to represent every example embodiment or every implementation within the scope of the current or future Claim sets. The figures and Detailed Description that follow also exemplify various example embodiments. Various example embodiments may be more completely understood in consideration of the following Detailed Description in connection with the accompanying Drawings.
One or more embodiments will now be described by way of example only with reference to the accompanying drawings in which:
In wireless communication systems, multiple well-separated antennas can be used for radio transmission at the same time on the same frequencies to increase the performance of these systems. These transmissions could be employed with multi antenna processing techniques and/or antenna diversity schemes such as: transmit diversity schemes; Cyclic delay diversity; Alamouti techniques; Multiple-Input Multiple-Output (MIMO) techniques; and beamforming techniques, to further enhance the performance. Receivers rely in general on the possibility that the RF signals transmitted over multiple antennas are well aligned in time and/or frequency in order to be able to receive and properly decode the transmitted signals.
In some transmitter architectures, multiple transmitters can be co-located (e.g. on the same chip, Printed Circuit Board (PCB) or module) and share the same time/frequency reference or clock. However, expensive cables are then needed to transport the RF signals from each transmitter to the antennas. To benefit from transmit diversity schemes, antennas should be well-separated, which makes these cables lengthy and therefore even more expensive.
In a distributed transmitter architecture, the RF signal for each antenna can be generated by a separate transmitter that is preferably located close to its associated antenna. By generating the RF signal close to the antenna no, less, or shorter expensive cables are needed to transport the RF signal from each transmitter to each antenna.
In a distributed architecture, each transmitter can have its own independent time/frequency reference (e.g. a signal from an oscillator or clock). Since the antenna/transmitter combinations can be well-separated, sharing/locking the oscillators of the transmitters would require an extra costly interface and/or expensive cables. A potential problem is that cost-effective oscillators may deviate too much from each-other and cause a lack of adequate alignment between transmitted signals. This can cause receivers, that do not anticipate this, to have problems with receiving the signals transmitted by these multiple transmitters. Receivers could have problems due to the resulting carrier frequency offset (CFO), sampling frequency offset (SFO) between the transmitters, and transmission time offset (offsets between the multiple transmitters) caused by oscillator offsets, which in turn cause the receivers to experience undesirably higher error rates. Further details are provided below.
It may not be straightforward to ensure adequate synchronization/alignment among distributed transceivers, which is advantageous in order to realize time and/or frequency aligned transmissions, such as for transmit diversity schemes.
This disclosure provides new ways to synchronize the time and/or frequency of a plurality of distributed Radio Frequency (RF) transceivers with independent time and/or frequency references (such as independent oscillators), by wirelessly exchanging RF signals or by synchronizing on transmitted RF frames. In this way, a plurality of transmitters can be capable of transmitting overlapping (in both time and frequency) signals that can effectively add up in the air to form together a desired signal for a receiver, that can be received without significant alignment problems. This can be part of a transmit diversity scheme and/or an antenna diversity scheme, for example.
Each of the distributed transceivers 102a-n includes at least one RF transmitter and at least one RF receiver. The transmitters and receivers can share or be locked to the same time and/or frequency reference (for example, one derived from a local oscillator). They are also able to share information with each-other, such as coordination signalling as will be described below. Such information can be shared via a digital interface or wirelessly. These transceivers may also be referred to as sub-systems of a distributed system.
The first-transceiver 102a can transmit a first-transmission-signal 104a, and the second-transceiver 102b can transmit a second-transmission-signal 104b. While the system 100 has N transceivers 102a-n arranged to transmit N transmission-signals 104a-n, other similar systems can have only two transceivers or any other larger number of transceivers.
The first-transmission-signal 104a can correspond to the second-transmission-signal 104b. For example, the first-transmission signal 104a may be representative of an information signal, while the second-transmission signal 104b is also representative of the same information signal. Both the first-transmission signal 104a and the second-transmission-signal 104b may thereby contain the same information content, corresponding to the information signal such that they constructively combine when received at a remote receiver.
In this way the system 100 of
In other examples, the first-transmission-signal 104a and the second-transmission-signal 104b may be transmitted at slightly different times, as part of a beamforming or phased-array system for instance. In such cases, transmission at different times is an example of aligned transmission as differences in the times of transmission can be carefully controlled with respect to one another to achieve a desired effect.
When the transceivers 102a-n are synchronized (with respect to time and/or frequency), each transmitter in a transceiver 102a-n is able to perform a time and/or frequency aligned transmission together with its counterpart transmitters in the other transceivers. The reception performance of receivers (remote), that want to receive the aligned transmissions from transceivers/sub-systems 102a-n and are not designed to cope with misalignment between transmission times/frequencies, should not be affected if synchronization is achieved within an acceptable alignment error margin.
Solutions to the problem of aligning, or synchronizing, multiple transceivers disclosed herein include wirelessly sharing synchronization signals between the different transceivers. Several different architectures can be used to achieve alignment, as disclosed further below.
In this example architecture 200, alignment-signalling 204a-n is shared between each of a plurality of transceivers 202a-n over a wireless communication channel by using one or more available RF receivers and transmitters within each transceiver 202a-n. This transmission could occur with very low transmit power or even be below the noise floor (i.e. using spread spectrum communication or ultra wideband (UWB) communication) in some examples. The plurality of transceivers 202a-n can also optionally share additional information wirelessly, such as coordination-signalling and other timing information as discussed below.
In this way, the transceivers may be able to satisfactorily synchronize/align with each other, without requiring feedback from the receiving party and without requiring a wired connection between them.
The first-transceiver 302 includes a time/clock-generation-unit (time/frequency reference sharing/synch) that provides one or more frequencies and/or time references for the first-transceiver 302. Similarly, the second-transceiver 304 includes a second-time/clock-generation-unit 306.
The frequency synthesizer 309 includes a frequency reference, which in this example is a crystal oscillator 330. In some examples, the crystal oscillator 330 is provided with temperature control for stability. The crystal oscillator 330 can provide a reference frequency of 40 MHz and an accuracy of <=20 ppm in this example. The IEEE 802.11 standard requires this accuracy. It will be appreciated that using a more accurate oscillator would be more expensive.
The frequency synthesizer 309 derives several frequencies from the reference frequency that is provided by the crystal oscillator 330. For example, phase locked loops (PLLs) can be used to derive one or more of the following frequencies: a frequency for the system timer 310, an RF carrier frequency, a digital-to-analogue (DA) converter frequency, an analogue-to-digital (AD) converter frequency, CPU clock frequency, DSP clock frequency, etc.
Globally one can write the relation between a derived frequency (fi) and the reference frequency fref as fi=Ni*fref/Mi, where Ni and Mi are the divider settings of the corresponding phase locked loop (PLL_i).
For the two or more transceivers, it can be important to have a sufficiently small offset between at least some of the derived frequencies. A possible reason for the presence of an offset is due to an inaccuracy of the crystal oscillator 330.
The system timer 310 can be implemented as a modulo counter running on the system timer frequency, running from 0 up to C−1. For the two or more transceivers, the system timers 310 should: (i) run on the same system timer frequency; and (ii) should have the same phase. In relation to “phase”: that is, at a given instant in time the system timers 310 of each of the transceivers should have the same value (or the discrepancy should be sufficient small). If the system knows the discrepancy of the counter values, then it can correct for the discrepancy by presetting the counter to a specific value.
There are several ways to correct compensate for offsets as will be discussed below.
Returning to
The second-transceiver 304 is similar to the first-transceiver 302, so the second-transceiver 304 and its component parts will not be described further here.
It will be appreciated that the designations of components herein as being ‘first’ or ‘second’ (as in first-time/clock-generation-unit 316 and second-time/clock-generation-unit 306 above) does not imply any structural or chronological limitation, and simply serves to identify which components are part of which transceiver. Accordingly, the first-transceiver 302 can transmit a wireless first-alignment-signal, representative of a state of the first-time/clack-generation-unit 316, to the second-transceiver 304 for reducing an alignment-error between the second-time/clock-generation-unit 306 and the first-time/clock-generation-unit 316.
More generally, an Nth-transceiver can transmit a wireless Nth-alignment-signal, representative of a state of an Nth-time/clock-generation-unit in the Nth-transceiver for reducing an alignment error between the Nth-time/clock-generation-unit and an Mth-time/clock-generation-unit in an Mth-transceiver that receives the Nth-alignment-signal (where N and M serve as indexes for any respective transceivers in a transceiver system containing 2 of more transceivers).
The first-transceiver 302 can set one or more parameters associated with the first-time/clock-generation-unit 316, based on the wireless second-alignment-signal 320, to reduce an alignment-error between the first-time/clock-generation-unit 316 and the second-time/clock-generation-unit 306. If there is a significant difference between the first-time/clock-generation-unit 316 and the second-time/clock-generation-unit 306 then setting the first-time/clock-generation-unit 316 can mean adjusting a parameter or setting in order to change the time and/or the frequency of the first-time/clock-generation-unit 316. Examples of such adjustments are described above. In this way, the alignment-error, that is, the difference in a time and/or frequency of the first-time/clock-generation-unit 316 and the second-time/clock-generation-unit 306, can be reduced. It will be appreciated that if there is no significant alignment-error then the first-time/clock-generation-unit 316 may not need to be adjusted.
The first-transmitter 312a can transmit a wireless first-transmission-signal 303a for a remote receiver via the antenna 318, in accordance with a time and/or frequency of the time/clock-generation-unit 316 once it has been aligned, as part of an antenna diversity scheme. Transmission of the first-transmission-signal can therefore occur at a time determined by a state of the time/clock-generation-unit 316 and/or using a carrier and sampling frequency derived from the time/clock-generation-unit reference (e.g. a crystal oscillator within the time/clock-generation-unit). Similarly, a transmitter of the second-transceiver 304 can transmit a wireless second-transmission-signal 303b for the remote receiver in accordance with a time and/or frequency of the second-time/clock-generation-unit 306, as part of the antenna diversity scheme. In this way, the antenna diversity scheme comprises aligned transmission of both the first-transmission-signal 303a and the second-transmission-signal 303b.
The frequency synthesizer 409 processes a clock-source-signal that is provided by an oscillator (such as a crystal oscillator as described above) and generates signals with different frequencies. These signals include: (i) a signal with a carrier frequency that is provided to the tuners of the transmitter 415 and the receiver 417; (ii) a signal with a sampling frequency (or digital signal processing frequency) that is provided to the DAC of the transmitter 415 and the ADC of the receiver 417; and (iii) a signal with a system timer frequency that is provided to the system timer 410.
The SFO is an offset between the sampling frequency of each distributed transmitter, which is equivalent to a difference in sample period. When the sample period is not the same, transmitted samples from each transmitter can get increasingly misaligned over time during a frame transmission, which can have negative effects on the receiver.
The CFO is a carrier frequency offset between two transmitters that provide the aligned transmission-signals as part of an antenna diversity scheme. Since the remote receiver experiences the combined signal of multiple transmission-signals it may not be able to correct for the separate carrier frequency offsets from the multiple transceivers. If the carrier frequency offset between the multiple transmission-signals is sufficiently small, the remote receiver will not suffer from it.
In some examples, the frequency synthesizer 409 can derive the carrier frequency, sample frequency and the system timer frequency from one reference frequency. In which case, these frequencies have a known relation to each other. Therefore the transceiver 400 can estimate a carrier frequency offset as discussed below, and then determine the offsets of the other frequencies unambiguously. For example, estimating the CFO can be less complex in some applications, and therefore the transceiver can determine the SFO based on an estimated CFO, and then correct for it.
In some applications, the SFO effects can have much less impact than the CFO effects. This is because, in general the sampling frequency is much less than the carrier frequency (fs<<fc). In some systems, the impact of SFO could be insignificant and such that it is not necessary to correct for SFO.
In this example, the system timer 410 is a component that counts periods of the input clock signal received from the frequency synthesizer 409 to generate a reference of elapsed time. This elapsed time can be used to time transmissions, amongst other things. In a distributed system, the system timer 410 should be synchronized in order the align the frame transmissions (in time) of the various distributed transmitters.
In this example, the transceiver 400 receives wireless (RF) signals 427 at its antenna 418. The RF signals 427 are representative of a state of the time/clock-generation-unit of the transmitter that sent them. The receiver 417 within the transceiver 400 can therefore determine information about properties of the RF signal 427. As discussed below it can estimate an offset between: (i) its system timer 410 (that provides the timing information for transmitting a transmission-signal) and (ii) a time/clock-generation-unit that provided a time and/or frequency reference at the transmitter that sent the RF alignment signal 427. Additionally, or alternatively, the receiver 417 can estimate an offset between (iii) its frequency synthesizer 409 (that provides frequency information for transmitting a transmission-signal) and (iv) a time/clock-generation-unit that provided a time and/or frequency reference at the transmitter that sent the RF alignment signal 427.
When these offsets are known, any SFO/CFO and timer clock skew can be counteracted as will be discussed below. For example, correlation techniques can be used to determine these offsets. Example properties of the received RF signal 427 that can be used for this purpose can include a predetermined part or parts of the RF signal 427, or a known repetition of the RF signal 427. These properties could be pre-defined or communicated as coordination-signalling via an available communication channel, which could be either wireless or hard-wired.
The Rx time estimation block 411 can generate a ToA-signal 405 that is representative of the time of arrival (ToA) of the RF signal 427 (according to the time base of the receiving sub-system).
In some examples, the transmitting transceiver can provide the time-of-transmission (according to the time base of the transmitting sub-system) to the transceiver 400 via an available communication channel (which can be wireless or wired), for example as part of a coordination-signal. This time-of-transmission can be provided as a count-value of the system timer of the transmitting transceiver, at the instant in time that the transmission was made. This count-value can also be referred to as an elapsed time of the transmitting sub-system at time of transmission.
A delay between the time-of-transmission and the time-of-reception of the RF alignment signal 427 can be determined at the transceiver 400 from round-trip time-of-flight measurements or can be predefined by calibration. The transceiver 400 can then determine a time reference signal 407, which is representative of an expected time-of-reception according to the time base of the transmitting sub-system, as the sum of the time-of-transmission (according to the transmitting sub-system) and the delay between transmission and reception. The time reference signal 407 can be provided by a digital interface, as shown in
The transceiver 400 can process (i) the expected time-of-reception according to the time base of the transmitting sub-system (provided as time reference signal 407), and (ii) the time-of-reception according to the time base of the transmitting sub-system (provided by the ToA-signal 405). The transceiver 400 can then generate an estimated time offset signal 412, representative of the system timer time offset, as the difference between: (i) the time-of-reception according to the system timer of the transmitter that transmitted the RF signal 427, and (ii) the time-of-reception according to the system timer of the receiver 417.
It will be appreciated that in other examples, the transceiver 400 can achieve the same result by subtracting the delay between transmission and reception from the time-of-reception according to the time base of the receiving-sub-system, and then comparing the time-of transmission according to the time bases of the transmitting- and receiving-sub-systems.
The estimated time offset signal 412 is provided to the system timer 410 such that it can reduce minimize its time offset to the system timer of the second transceiver and generate a reference of elapsed time that is used by the transmitter 415 to time transmissions aligned with the second transceiver.
The CFO estimation block 413 generates an estimated carrier frequency offset signal 421, from which a timer frequency offset between the local system timer 410 and the remote system timer (such as a second system timer, not shown) that was used by the transmitter to trigger the sending of the RF signal 427 can be determined. The estimated frequency offset signal 421 is provided to the system timer 410 such that it applies a clock skew correction to the system timer 410 to reduce the timer frequency offset. That is, if the system timer 410 counts too fast or too slow (i.e. there is a clock skew), due to an input signal with frequency offset, the transceiver 400 can correct this by causing the system timer 410 to count faster/slower based on the estimated frequency offset signal 421. The estimated carrier frequency offset signal 421 relates to the timer frequency offset in this example because a single oscillator is used to provide a clock-source-signal to the frequency synthesizer 409, and the system timer 410 is used for both the transmitter 415 and the receiver 417.
The CFO estimation block 413 also provides the estimated frequency offset signal 421 to the frequency correction block 419 of the transmitter 415. In this way, the transmitter 415 can correct the carrier frequency and/or sampling frequency of the signals that are to be transmitted, thereby correcting CFO and/or SFO.
The functionality described above and illustrated in
The Rx time estimation block 411 generates a T A-signal that is used in the same way as for
The CFO estimation block 425 generates an estimated frequency offset signal 424 in the same way as for
In this way, transceiver B 420 can indirectly tune the system timer 422 to reduce/minimize its timer frequency offset/clock skew using the estimated frequency offset signal 424 provided by the CFO estimation block 425.
The alignment and/or synchronization processing that is described with reference to
It will be appreciated that
In accordance with the architectures discussed above in relation to
One or more of the architectures of
The present disclosure proposes new ways to synchronize time and frequency of multiple distributed RF transceivers with independent time and/or frequency references (e.g. oscillators) to enable time and/or frequency aligned multiple antenna transmissions such that they constructively combine when received at a remote receiver. Two different approaches for providing wireless alignment-signals for synchronization or alignment of distributed transceiver-systems are disclosed below. The two approaches can be used individually or in combination.
The first approach is disclosed in relation to
The second approach is disclosed in relation to
A wireless RF first-alignment-signal 604 which in this example is dedicated for alignment/synchronization, is transmitted by the first-transceiver 602a. (In this example the first-transceiver 602a transmits the alignment signal, but it will be appreciated that the transmission can be provided by a different transceiver for any given period of time). The other transceivers 602b-n receive this RF first-alignment-signal 604 and determine the offsets of their time/clock-generation-units with respect to the first-alignment-signal 604 and compensate for it. The properties of the first-alignment-signal 604 that the receiving transceivers 602b-n need for the offset estimation are pre-defined in this example.
When the transceivers 602a-n have been aligned/synchronized, they can each transmit a respective block of data 616a-n to a remote receiver. These blocks of data 616a-n can be called frame transmissions. Since each frame transmission 616a-n, for a given period of time, provided by each transceiver 602a-n is aligned with one another, the quality of the signal received by the remote receiver can be significantly improved with a consequently reduced error rate.
In subsequent time periods, the Nth-transceiver 602n can transmit an Nth-alignment-signal 618 and the second-transceiver 602b can subsequently transmit a second-alignment signal 620.
Depending on the architecture of transceiver-system employed, the transmitter used to transmit the alignment signal for each different period of time can be chosen by a central controller, or by negotiation of the transceivers via an available wireless or hard-wired digital communication channel, or can be pre-defined.
Carrier-Sense Multiple Access with Collision Avoidance (CSMA-CA) like protocols can be used to reduce interference with other systems or to comply with regulations. The wireless transmission of alignment-signals described herein can advantageously be performed with a very low transmit power and can even be below the noise floor (i.e. spread spectrum, ultra wideband (UWB)) to reduce interference. For example, when the transceiver system antennas are located close to each other, relative to the range between the transceiver system and other remote system with which the transceiver system may communicate. By use of a suitable communication channel, coordination signalling can be provided to the other transceivers so they can be made aware of when to expect the alignment/synchronization signals. This can increase the chance for successful reception with reduced error rates.
In this way, the transceivers 702a-n can synchronize to an average of the time and/or frequency reference of the plurality of simultaneously transmitted alignment-signals by synchronizing to a RF alignment signal coming from a plurality of different transceivers.
As discussed above, which of the transceivers will perform the alignment-signal transmission and which of the transceivers will set their time/clock-generation-units to improve alignment/synchronization can be pre-defined. Alternatively, coordination-signalling can be exchanged between the transceivers or received from a central controller to define which of the transceivers operate as a master, and which operate as a slave.
An alternative to the above approach of using an alignment-signal specifically created for the purpose of aligning the time/clock-generation-units of different transceivers can involve different transceivers using frames transmitted by one or more of the transceivers for alignment purposes. In these examples, the frames contain data to be transmitted to a distant receiver but can also, in addition, be used for alignment purposes.
For instance, by determining the last time that synchronisation was carried out. In some examples, a distributed multi-transceiver system can perform single antenna and/or multi antenna transmissions in normal operation.
The single transmission of the first frame 904a-n, can be received at a remote receiver 904a, the second transceiver 902b, and the Nth transceiver 902n. The second transceiver 902b and the Nth transceiver 902n can use the first frame 904b-n to align their respective time/clock-generation-units with the time/clock-generation-unit in the first transceiver 902a, for example as discussed above. Then, all of the transceivers 902a-n of the multi-transceiver system 900 can transmit a second frame 920a-n with satisfactory alignment in time and/or frequency.
Subsequently, the transceivers can be re-synchronized/re-aligned based on a frame that is transmitted by a different transceiver—for example a frame 940n transmitted by the Nth transceiver 902n.
In some examples, the wireless alignment-signal can be based on an earlier-Nth-transmission-signal 940n (where N can be any number greater than one). In this example, the alignment/synchronisation of the first-transceiver 902a can take place during a particular time-slot 940a. Once the multi-transceiver system 900 has been aligned, it can transmit a first transmission signal 950a, a second transmission signal 950b and an Nth transmission signal 950n. Since the first transceiver uses the frame 940n transmitted before the Nth transmission signal 950n, that frame 940n can be called the earlier-Nth-transmission-signal.
In some examples, the multi-transceiver system may have a controller configured to determine an alignment-error associated with a transceiver. If the alignment error is greater than a predetermined threshold, then the transceiver can set the first-time/clock-generation-unit based on a wireless alignment-signal.
For instance, the controller may compare signalling representative of a first-transmission-signal 930a and signalling representative of an Nth-transmission-signal 930n to determine an alignment-error. If the alignment error is greater than a predetermined threshold, then the first-transceiver 902a can set the first-time/clock-generation-unit based on an Nth-transmission-signal 940n. In some examples, the controller may simply compare timing/frequency information received as part of a received alignment-signal or transmission signal with information about a local time/clock-generation-unit.
For a particular time-slot during which alignment is performed, the first transceiver 902a can be de-activated by not transmitting any first-transmission signal. This can improve the first-transceivers 902a ability to receive the earlier-Nth-transmission-signal 940n for alignment purposes.
To ensure well aligned/synchronised transmissions, a transceiver can be controlled such that it does not join in certain multiple antenna transmissions; for example if a component in the system determines that the transceiver is not sufficiently well synchronized. This determination could be negotiated among transceivers or determined by a central control unit. If a transceiver does not transmit a frame, then it may be configured to receive and process a frame from one or more of the other transceivers and then synchronize/align its time/clock-generation-unit based on the frame(s) from the other transceiver(s).
An advantage of the alignment solutions described herein is that hardware can be reused. Furthermore, these solutions do not necessarily require an extra wired interface, any feedback from the receiving party, the availability of a GPS signal or a base station.
The embodiments described in relation to
The instructions and/or flowchart steps in the above figures can be executed in any order, unless a specific order is explicitly stated. Also, those skilled in the art will recognize that while one example set of instructions/method has been discussed, the material in this specification can be combined in a variety of ways to yield other examples as well, and are to be understood within a context provided by this detailed description.
In some example embodiments the set of instructions/method steps described above are implemented as functional and software instructions embodied as a set of executable instructions which are effected on a computer or machine which is programmed with and controlled by said executable instructions. Such instructions are loaded for execution on a processor (such as one or more CPUs). The term processor includes microprocessors, microcontrollers, processor modules or subsystems (including one or more microprocessors or microcontrollers), or other control or computing devices. A processor can refer to a single component or to plural components.
In other examples, the set of instructions/methods illustrated herein and data and instructions associated therewith are stored in respective storage devices, which are implemented as one or more non-transient machine or computer-readable or computer-usable storage media or mediums. Such computer-readable or computer usable storage medium or media is (are) considered to be part of an article (or article of manufacture). An article or article of manufacture can refer to any manufactured single component or multiple components. The non-transient machine or computer usable media or mediums as defined herein excludes signals, but such media or mediums may be capable of receiving and processing information from signals and/or other transient mediums.
Example embodiments of the material discussed in this specification can be implemented in whole or in part through network, computer, or data based devices and/or services. These may include cloud, Internet, intranet, mobile, desktop, processor, look-up table, microcontroller, consumer equipment, infrastructure, or other enabling devices and services. As may be used herein and in the claims, the following non-exclusive definitions are provided.
In one example, one or more instructions or steps discussed herein are automated. The terms automated or automatically (and like variations thereof) mean controlled operation of an apparatus, system, and/or process using computers and/or mechanical/electrical devices without the necessity of human intervention, observation, effort and/or decision.
It will be appreciated that any components said to be coupled may be coupled or connected either directly or indirectly. In the case of indirect coupling, additional components may be located between the two components that are said to be coupled.
In this specification, example embodiments have been presented in terms of a selected set of details. However, a person of ordinary skill in the art would understand that many other example embodiments may be practiced which include a different selected set of these details. It is intended that the following claims cover all possible example embodiments.
Koppelaar, Arie, Van Splunter, Marinus, Filippi, Alessio, van Meurs, Lars
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